This invention relates to a passive (self-pumped) phase conjugate mirror and to its use as an end mirror in a laser resonator for correction of intracavity phase distortion.
The concept of phase conjugation is well known and described in the literature. This has application in many systems for imaging through distorting media using phase conjugation by four-wave mixing, thereby to correct the distortion. A particular application is in providing a reflecting mirror to assist in the buildup of oscillation in a CW laser.
The technology of a phase conjugate mirror (PCM) is a branch of phase conjugate optics (PCO) which uses nonlinear optical media. For a tutorial paper on PCO used to perform a variety of optical functions, such as PCM's, see A. Yariv, IEEE J. Quantum Electron. QE-15, 650 (1978).
In the past, PCM technology was based either upon stimulated scattering processes, such as stimulated Brillouin scattering (SBS) or stimulated Raman scattering (SRS), or upon four-wave mixing in third-order optically nonlinear media using one or two high-quality external pumping beams. A major disadvantage of the SBS or SRS method was its associated high light intensity threshold, typically megawatts per cm.sup.2, while a major disadvantage of the four-wave mixing method was a requirement for coherence of the pumping beams with the incident signal beam from a coherent light source, such as a laser. An object of this invention is to provide a passive (self-pumped) phase conjugate mirror (PPCM) free of these limitations.